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Intego security alert: Apple Remote Desktop Vulnerability

June 2008 by Intego Security Alert

Allows Malicious Programs to Execute Code as Root

Exploit: ARDAgent root privilege escalation

Discovered: June 19, 2008

Risk: Critical

Description: A vulnerability has been discovered that allows malicious programs to execute code as root when run locally, or via a remote connection, on computers running Mac OS X 10.4 and 10.5. This vulnerability takes advantage of the fact that ARDAgent, a part of the Remote Management component of Mac OS X 10.4 and 10.5, has a setuid bit set. Any user running such an executable gains the privileges of the user who owns that executable. In this case, ARDAgent is owned by root, so running code via the ARDAgent executable runs this code as root, without requiring a password. The exploit in question depends on ARDAgent’s ability to run AppleScripts, which may, in turn, include shell script commands. When an application enables a root privilege escalation of this type, any malicious code that is run may have devastating effects. These may range from deleting all the files on the Mac (regardless of who owns them) to more pernicious attacks such as changing system settings, and even setting up periodic tasks to perform them repeatedly. Any application could use this vulnerability to obtain root privileges without users ever needing to enter passwords. Users could run malicious programs that they download from the Internet or receive from friends or colleagues, and, if the program exploits this vulnerability, simply launching it once would be sufficient for damage to be done.

There are cases where this exploit does not work. If a user has turned on Remote Management in the Sharing pane of System Preferences under Mac OS X 10.5, or if a user has installed Apple Remote Desktop client under Mac OS X 10.4 or earlier and has activated this setting in the Sharing preferences, the exploit will not function. Most users, however, will not have this service turned on; generally only those users who want to observe or control other computers on their network will turn this on to do so. Note that Mac OS X 10.5’s Screen Sharing function has no effect on this vulnerability. This exploit can be triggered by any type of user account: standard user, administrator, or even a guest account. Therefore, a guest logged in using Mac OS X 10.5’s Guest Account feature has the ability to download an application and unwittingly run malicious code with no security warning. Means of protection: The best way to protect against this exploit is to run Intego VirusBarrier X5 with its virus definitions dated June 19, 2008. VirusBarrier X5 will perform an action that will deactivate ARDAgent’s ability to run AppleScripts. Intego recommends that users never download and install software from untrusted sources or questionable web sites.

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